The present invention relates to an optical character recognition system having a controllable light source for illuminating an object such as a credit card, paper tag, container and the like bearing indicia to be read. In particular, the present invention is directed to a method and apparatus for controlling the light source to illuminate an object having indicia to be read at a relatively high light intensity and to maintain said high light intensity during the reading of the indicia on the object, and to reduce the light intensity to a low level after the indicia is read.
It is known in the prior art to automatically operate a light source at a plurality of light intensities in response to light reflected from an object. For example, U.S. Pat. No. 3,631,250, entitled Optical Positive Feedback Sensor Circuit, issued to Van Buskirk, describes an apparatus for this purpose. A single photodetector senses the light reflected by coded information on an object and controls a positive feedback loop which determines the intensity at which the object is illuminated. The positive feedback loop includes a series of cascaded transistors which are operated either in a quiescent state or in saturation. Any light reflected from the coded information on the object is sensed by the detector which causes the positive feedback loop to seek a non-linear condition, such as saturation. In the non-linear condition, the positive feedback loop causes the object to be illuminated at the maximum light intensity. If, however, no light is reflected from the object, the sensor drives the positive feedback loop in the quiescent condition. In the quiescent condition, the positive feedback loop causes the object to be illuminated at the minimum light intensity.
Such a device is suited for use with an object comprising shapeless coded indicia in the form of reflective and non-reflective surfaces. Where, however, the shape of the indicia must be identified, for example, where the indicia are alpha-numeric characters, such a device is inadequate. In that case, it is well known that a plurality of detectors is required to sense specific portions of each character to properly identify the character. Although a single detector may be used to indicate the presence of characters, it cannot be used to distinguish between characters. Furthermore, in reading a plurality of characters it is necessary to control the duration of the high light intensity and maintain this intensity during reading, which the device in U.S. Pat. No. 3,631,250 cannot do.
In a character recognition system, the shape of the indicia is important and the absence of reflected light is an essential piece of information for identifying the indicia. In addition, the absence of reflective light may indicate that the object is not being illuminated at all and only ambient light is being detected. In that case, it is desirable to rapidly recognize this condition and then reduce the light intensity to a low level. A device such as the one described in U.S. Pat. No. 3,631,250 is entirely unsuitable for this purpose. In such a device, should a detector sense reflected or ambient light, the object will be illuminated at the maximum light intensity. Thus, such a device cannot distinguish between true reflections and spurious reflections on strong ambient light, and therefore, cannot adequately control the light intensity for character recognition.
In character recognition systems, the shape of each character must be sensed. For this purpose, character recognition systems employ a plurality of detectors for sensing the non-reflective portions of the character as well as the reflective portions of the object which bear the characters. At the time that characters are to be read, it is desirable to use a relatively high light intensity. However, during all other times, it is desirable to use a relatively low light intensity.
By illuminating the character at a relatively high light intensity only when characters are to be read, the lifetime of the source of illumination can be increased and the deleterious effects of heat dissipation on other components of the system placed in proximity to the source of illumination can be minimized. Furthermore, since the source of illumination may be located in a portable wand which is manually transported past the characters to be identified, continuously operating the source at a relatively high level of intensity may cause the wand to heat up, causing discomfort to the operator and, in the extreme, preventing further manual transportation of the wand. To prevent such discomfort, the source should be operated at the relatively high level of intensity only when characters are to be identified.
Although the source of illumination in a character recognition system may be manually controlled to ameliorate the effects described above, it is well known that manual operation can prove cumbersome and can frequently be attended by operator error. It is therefore desirable to control the light intensity at which characters are illuminated and the duration thereof automatically and without any intervention by an operator.
Moreover, character recognition systems often include rather elaborate and detailed components and, for the sake of economy, it is desirable that any auxiliary control equipment be relatively simple and flexible. In particular, it is desirable that an auxiliary system for automatically controlling the light intensity at which characters are illuminated and the duration of such intensity be simple and flexible, using as much of the subsisting character recognition system as possible.
A primary advantage of the present invention is that it automatically controls the intensity of a light source with which an object bearing indicia is to be illuminated and the duration of such intensity without operator intervention.
A further advantage of the present invention is that it controls the intensity of a light source with which an object is to be illuminated and the duration of such intensity using relatively simple and flexible components to allow for easy adjustment to a variety of operating conditions.
A still further advantage of the present invention is that it controls the intensity of a light source with which an object is to be illuminated without introducing redundant and unnecessary equipment, that is, by using subsisting portions of a character recognition system.
Another advantage of the present invention is that it increases the lifetime of the source of illumination and eliminates the deleterious effects of heat dissipation of components of the system located proximately thereto.
Other advantages of the present invention appear hereinafter.